JP2938554B2 - Optical displacement measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement measuring device for measuring the surface roughness and displacement of a surface to be measured such as the surface of a workpiece.

[Conventional technology]

As a conventional optical displacement measuring device, for example,
Some are disclosed in, for example, Japanese Patent Publication No. 210305 and Japanese Patent Publication No. 60-186705.

FIG. 3 shows an optical displacement measuring device disclosed in JP-A-59-210305, in which a light beam 2 radiated from a laser light source 1 is changed to a predetermined beam diameter by a beam expander 3. 1/4 through the beam splitter 4
The light is irradiated onto the surface 8 to be measured of the object 7 via the wave plate 5 and the condenser lens 6.

The return light reflected by the surface 8 to be measured is reflected by the beam splitter 4 through the condenser lens 6 and the quarter-wave plate 5, and
The return light 9 is split into two by a total reflection mirror 10 for splitting the wavefront, and passes through condensing lenses 11 and 12, respectively.
, And is received.

Each of the displacement detectors 13 and 14 is a two-divided optical detection element 1
3a, 13b; 14a, 14b, the outputs of which are subtracted by subtractors 15, 16 and then added by an adder 17.

In such an optical displacement measuring device, when the measured surface 8 is in a focused state where the focusing lens 6 is in focus, the return light 9 becomes a parallel light flux as shown by a solid line in FIG.
On 3 and 14, a circular light spot is formed. Therefore, in this in-focus state, the two-part optical detection element 13a,
13b; If the dividing lines of 14a and 14b are aligned with the central axis of the light spot, the amount of light incident on each optical detection element becomes equal, so that the outputs of the subtracters 15 and 16 become zero and the adder 1
The output of 7 also becomes zero.

When the object 7 moves x in the + direction in FIG. 3 from this in-focus state, the return light 9 on the surface 8 to be measured becomes divergent light as shown by a two-dot chain line in FIG. The central axes of the light spots formed on the displacement detectors 13 and 14 are shifted toward the optical detection elements 13a and 14a. Therefore, the optical detection element 13
The received light amount of the optical detectors 13b and 14b decreases, the differential outputs of the subtracters 15 and 16 increase to the positive side, and the output of the adder 17 also increases in the positive direction. Will increase.

On the other hand, when the object 7 moves in the opposite direction, the return light 9 on the surface 8 to be measured becomes convergent light as shown by a dotted line in FIG. The center axis of the light spot to be shifted is shifted toward the optical detection elements 13b and 14b. Therefore, the amount of light received by the optical detection elements 13a and 14a decreases, the amount of light received by the optical detection elements 13b and 14b increases, and the differential outputs of the subtractors 15 and 16 increase to the minus side. The output will also increase in the negative direction.

As described above, the output of the adder 17 changes in the opposite direction around the in-focus state in accordance with the displacement of the surface 8 to be measured, whereby the displacement of the surface 8 to be measured can be measured.

In addition, at such an optical displacement measurement position, if the movement of the DUT 7 is tilted and the optical axis shifts, the light spot formed on the displacement detector 13 will shift from the focus position. In contrast, the optical spot formed on the displacement detector 14 moves by an amount obtained by subtracting the optical axis deviation from the deviation from the in-focus position. By adding the outputs of the subtracters 15 and 16 by the adder 17, it is possible to cancel the optical axis deviation.
Therefore, only the displacement of the surface 8 to be measured can be measured without being affected by the optical axis deviation.

[Problems to be solved by the invention]

However, the above-described conventional optical displacement measuring device requires two sets of two-division displacement detectors (13, 14) and a condenser lens (11, 12), and thus the number of parts is increased. In addition, there is a problem that optical position adjustment is troublesome and cost is high.In addition, since it is necessary to use displacement detectors 13 and 14 and condenser lenses 11 and 12 having the same characteristics, it is necessary to select parts. There is a problem that the degree of freedom is reduced.

The present invention has been made in view of such a conventional problem, and a displacement amount can be measured by one set of a displacement detector and a condenser lens. Therefore, the number of parts can be reduced, and the degree of freedom in selecting parts can be reduced. It is an object of the present invention to provide an optical displacement measuring device appropriately configured so that the optical position can be easily adjusted and the whole can be made inexpensive.

[Means and actions for solving the problem]

In order to achieve the above object, according to the present invention, a first light condensing means for condensing linearly polarized light on a surface to be measured, and a polarization plane conversion means for selectively switching a polarization plane of return light from the surface to be measured. One has a polarizing film that transmits P-polarized light and the other has a polarizing film that transmits S-polarized light, and a wavefront splitting means for splitting a light flux transmitted through the polarization plane converting means into a wavefront; A second light condensing means for emitting light, and a displacement detector having an optical detection element divided into two on the same surface and receiving a light beam condensed by the second light condensing means, Return light from the surface to be measured is alternately converted by the polarization plane conversion means so that its polarization plane becomes P-polarized light and S-polarized light with respect to the wavefront splitting means, and received by the displacement detector. Is configured to measure the displacement of the surface to be measured based on

〔Example〕

FIG. 1 shows a first embodiment of the present invention. In this embodiment, the light beam 22 emitted from the laser light source 21 is
Is changed to a predetermined beam diameter by a beam expander 23, and is incident on a polarization beam splitter 24. The P-polarized light transmitted through the polarization beam splitter 24 is converted into circularly polarized light by a quarter-wave plate 25, and a condensing lens. 26 causes the measurement surface 28 of the measurement object 27 to be irradiated.

The return light reflected by the surface to be measured 28 is
26, the light enters a quarter-wave plate 25, where it is converted into S-polarized light, reflected by a polarizing beam splitter 24, and its return light 29
Through the half-wave plate 30 to the polarization beam splitters 31 and 32 constituting the wavefront splitting means. The polarizing beam splitters 31 and 32 are integrally formed so that one side reflects P-polarized light and the other side reflects S-polarized light, and has an extinction ratio opposite to that of P-polarized light and S-polarized light. The return light 29 is arranged so as to be divided into two in a state where there is no.

The light transmitted through the polarization beam splitters 31 and 32 is received by a displacement detector 34 having optical detection elements 34a and 34b divided into two through a condenser lens 33, and the outputs of the optical detection elements 34a and 34b are subtracted by a subtractor 35. And store it in the memory 36.

In this embodiment, the half-wave plate 30 is driven by a motor 37 to selectively rotate its polarization plane, thereby alternately switching the light beam transmitted through the half-wave plate 30 to P-polarized light and S-polarized light. At the same time, in synchronization with this switching, under the control of the synchronizing circuit 38, the subtractor for each of the P-polarized light and the S-polarized light
The output of 35 is stored in the memory 36, and the P stored in the memory 36
Output of subtractor 35 for polarized light and subtractor 35 for s-polarized light
Is subtracted by the subtractor 39 from the output of

With this configuration, the surface to be measured can be output from the subtractor 39 without being affected by the optical axis deviation, as in FIG.
The polarity is inverted according to the displacement direction of 28, and a signal having an amplitude corresponding to the displacement amount can be obtained.

As described above, according to this embodiment, one set of the condenser lens 33 and the two-division displacement detector 34 are similarly covered without using two sets of the condenser lens and the two-division displacement detector. Measurement surface
Since the amount of displacement of 28 can be measured, the number of parts can be reduced, the degree of freedom in selecting parts can be increased, the optical position can be easily adjusted, and the whole can be inexpensive.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, a KDP crystal 41, which is one of electro-optic crystals, is used instead of the half-wave plate 30 of the first embodiment.
Apply a half-wave voltage from the power supply 42 to the phase difference of π,
Light incident on the polarization beam splitters 31 and 32 is alternately switched to P-polarized light and S-polarized light, and other configurations and operations are the same as those of the first embodiment.

Therefore, according to this embodiment, in addition to the effects of the first embodiment, the polarization plane is switched by using the KDP crystal 41. Therefore, when the polarization plane is switched by using a half-wave plate and a motor. In comparison, there is an effect that the device can be made more compact.

〔The invention's effect〕

As described above, according to the present invention, the return light from the surface to be measured is alternately switched with respect to its polarization plane by the polarization plane conversion means, one of which transmits P-polarized light and the other of which transmits S-polarized light. Through a wavefront splitting means and a focusing means having a film,
Light is received by a displacement detector having an optical detection element that is divided into two on the same surface, and the displacement of the surface to be measured is measured based on the output. Therefore, the light flux transmitted through the wavefront dividing means is collected. Only one focusing means and one displacement detector are required. Therefore, the number of components can be reduced, the degree of freedom of component selection can be increased, the optical position can be easily adjusted, and the entire device can be compared with the conventional case where two sets of light collecting means and displacement detector are used. It can be cheap.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of the present invention, FIG. 2 is a view showing the same second embodiment, and FIGS. 3 and 4 are views for explaining a conventional technique. 21 Laser light source 22 Light beam 23 Beam expander 24 Polarizing beam splitter 25 Quarter-wave plate 26 Condenser lens 27 DUT 28 DUT Surface 29 Return light, 30 Half-wave plate 31, 32 Polarizing beam splitter 33 Condenser lens, 34 Displacement detector 34a, 34b Optical detection element 35, 39 Subtraction , 36… Memory 37… Motor, 38… Synchronous circuit 41… KDP crystal, 42… Power supply

Claims (1)

(57) [Claims] A first condensing means for condensing linearly polarized light on a surface to be measured; a polarization plane converting means for selectively switching a polarization plane of return light from the surface to be measured; A wavefront splitting means for splitting the light flux transmitted through the polarization plane converting means into a wavefront, and a second light beam splitting means for collecting the light flux transmitted through the wavefront splitting means.
And a displacement detector having an optical detection element divided into two on the same surface and receiving a light beam condensed by the second light condensing means. Return light, the polarization plane is alternately converted by the polarization plane conversion means so as to be P-polarized light and S-polarized light with respect to the wavefront splitting means, received by the displacement detector, and based on the output, An optical displacement measuring device configured to measure a displacement of a surface to be measured.